Apparatus for electrostatically coating articles



June 4, 1957 w. A. STARKEY El'AL. 2,794,417

APPARATUS FOR ELECTROSTATICALLY COATING ARTICLES 2 Sheets-Sheet. 1

Original Filed Sept. 29, 1944 June 4, 1957 w. A. STARKEY EI'AL APPARATUSFOR ELECTROSTATICALLY COATING ARTICLES Original Filed Sept, 29, 1944 2Sheets-Sheet 2 United Sttes APPARATUS FOR ELECTROSTATICALLY COATINGARTICLES William A. Starkey (deceased), Columbus, and Edwin M. Ransburg,Indianapolis, Ind., assignors to Ransburg Electro-Coating Corp.,Indianapolis, Ind., a corporation of Indiana 4 Claims. (Cl. 118-51) Thisapplication is a division of our copending application Serial No.556,390, filed September 29, 1944, now Patent No. 2,685,536, grantedAugust 3, 1954. That patent describes a method and apparatus forelectrostatically coating articles with a liquid coating material suchas paint, lacquer, ink, wax and the like. Such articles to be coated maybe of either conducting or nonconducting material, may be structural incharacter or comprise fabric or paper sheets.

This application is particularly directed to forms of apparatus suitablefor use in carrying out methods claimed in our aforesaid patent.

In respect to the method of electrostatically coating articles bydischarging a spray of coating material from an air operated or airatomizing spray gun reference may be made to such prior patents as Pugh,No. 1,855,859, issued April 26, 1932, for Method and Apparatus forCoating Articles, and Ransburg and Green, Nos. 2,247,963 and 2,334,648,issued July 1, 1941, and November 16, 1943, for Apparatus for SprayCoating Articles and Method of Spray Coating Articles, respectively.However, in the use of spray guns or the like many disadvantages developin that the air operated spray gun is limited to a comparatively small'field of dispersion, but more important it causes the coating materialto be discharged in non-uniform sized particles, and in variablepatterns. Thus, there is an uneven dispersion of the coating particlesover the surface to be coated due to the inertia generated in thedischarge, causing the larger particles to travel further in the fieldthan the more finely divided particles. In some arrangements, dependingupon the direction of the discharge, a variable pattern of spray iscreated and reproduced on the surface to be coated, the heavier coatingparticles being caused to impinge over one area and the more finelydivided particles over another area. By reason of such variance it hasbeen found necessary in practice under certain conditions of coating toarrange a sizable battery of spray guns with particular regard to theirvariable patterns of coating application so that the several gunscomplement each other to even out the pattern as a battery.

It is the purpose of our invention to meet this problem of coatingarticles in an electrostatic field by eliminating the use of such sprayguns and employ in place thereof a-new method and apparatus forsupplying the coating material for electrostatic precipitation upon thesurface to be coated. This is accomplished by providing in the field aseries or plurality of small inert droplets of coating material andestablishing such electrostatic force in the field asto develop andtransmit finely divided particles of coating material from. saiddroplets to the surface of the article to be coated. In describing :as'inert the drops or droplets from which atomization takes place, it isour purpose to indicate that during the coating process each drop issupported on the head as above described, and that while the drop may becontinuously atent" Such method and apparatus has several importantadvantages over the spray gun arrangements heretofore employed.Thecoating material may be introduced into the electrostatic field by anapplicator head having a series of orifices through which the materialmay ooze in the form ofinert droplets. Such applicator head may besubstantially coextensive with the surface to be coated and thereby takethe place of a battery of sprayguns as heretofore employed. The dropletswill be developed into finely divided particles by the electrostaticforce so that all particles will be transmitted or precipitated upon thesurface to be coated uniformly over the entire surface.

A feature of the invention, as above described, resides in theapplicator head including formation of the discharge orifices thereinand the control of the rate of discharge ofthe material to form theinert droplets at approximately the rate of their electrostaticdischarge. Thus, depending upon the viscosity and other characteristicsof the material, the control of the applicator head will be such as topermit discharge of just the right quantity and size of the droplets toefiect the greatest efficiency in coating a surface.

The full nature of the invention will be understood from theaccompanying drawings and the following description and claims.

Fig. I is a diagrammatical illustration-showing one arrangement ofapplicator in respect to the article to be coated. Fig. 2 is a sectiontaken on the line 2-2 of Fig. 1. Fig. 3 is a perspective view ofa-modified form of applicator with a control handle associatedtherewith. Fig. 4 is a section taken on the line 44 of Fig. 3. Fig. 5isa perspective sectional view showing a portion of a furthermodification of the applicator head. Fig. 6 is the same as Fig. 5, takenon the line 6-6 thereof. Fig. 7 is a perspective view of a furthermodification of the applicator head in association with the surface tobe coated. Fig. 8 is a section taken on the line 88 of Fig. 7. Fig. 9 isa diagrammatical illustration of the circuit and one of the arrangementsof the applicator head relative to the article to be coated.

The invention is illustrated by one modification thereof in Figs. 1 and2 wherein there is shown an article 10 to be coated mounted or carriedupon a suitable support or conveyor 11 which is grounded at 12. Anapplicator head 13 is provided which is preferably substantiallycoextensive With the surface to be coated. Said applicator head may befixedly or adjustably mounted on a suitable support, or hand manipulatedby a handle 14. The applicator head, as indicated in Fig. 2, is V-shapedin cross section and along its reduced discharge end 17a it is provided.with a series of orifices 15 through which the coating materialindicated at 16 may be oozed out in the form of droplets 17. Theapplicator head maybe connected With'a source of supply of coatingmaterial by a flexible tube, there being herein illustrated threecompartments in the head, each connected with an individual source ofsupply 18 by a tube 19. The discharge edge 17:: has an extent many timesthe maximum crosssectional dimension of the passageways provided by thetube 19. Sufficient pressure will be created in the containers formingthe source of supply 18 for maintaining the material 16 in the headunder just the proper pressure to cause the droplets to ooze therefromas they are dispersed by the applied electrostatic force.

As illustrated, the applicator head is connected to a source of highvoltage indicated at 20 through one terminal thereof, the other terminalof said source being grounded at 21 and through ground connected with anarticle 10 to be coated. Accordingly, the space or field between theapplicator head and article .10 is electrostati fcally charged by reasonof the article being grounded and the applicator head being at highpotential. The eifect thereof is to cause an electrical force to act onthe droplets 17, causing them to be broken up into finely divided orminute particles of coatingfmate'rial, such as 'to beattracted to thegroundedarticle'for deposition thereon. Thus, the grounded article maybe referred to as a collecting electrode of one potential with theapplicatorhead serving as. a discharge electrode of adifierentpotential. It is found that the electrostatic force'set up in the fieldbetween the electrodes is such as to develop and transmit finely dividedparticles of'the droplets 17 from one electrode to the other. noted thatas the droplets are caused to slowly ooze from the applicator head theyare inactive or inert, but subject to being broken up into finelydivided particles and distributed over the surfaceofithe opposedelectrode.

In this connection it' will be The same action willtake placewherein theapplicator head may be grounded and the article directly connected withthe source .of high voltage and thus be charged at a high potential; I

' Another modification isiHustrated in Figs. 3 and 4,

wherein the applicatorhead 113 is adjustably supported Figs. 5 and 6show a further modification of the ap- V plicator head indicated at 213.In this head the orifices through which the coating material flows areprovided by a plate 214 clamped between opposed .rows or needles 215.The needles are cylindrical ,so that the material will be caused to flowbetween them, the plate 214 and the clamping walls 216 so as to come outin the form of an inert droplet 217 of coating material. As illustratedin the drawings, the needles aresufiiciently close together as to causethe coating. material to bridge the spaces therea between.

In the modification of Figs. 7 and 8 there is illustrated a groundedsurface 310 to be coated. This may be a continuously moving sheet ofpaper or any other article, it being understood that wherein sucharticle or material is non-conducting, it is carried by and on a supportor conveyor 311 of grounded conducting material. In this arrangement theapplicator head 313 is supported across and above the surface to becoated, and coating material is fed thereto through the valve controlledpipe 319 leading from the source of such material. .Said pipe extendsthrough the head, having a series of orifices or openings thereinthrough whichthe material may drip by gravity. Mounted on and connectedto a source of high voltage through the pipe 319, there is a supportingshield 314 extending downwardly and terminating below the pipe toprovide a frame for a wire wrapping 315. The coating materialaccumulates from the dripping s into a pocket formed by. the wirewrappings, as indicated at 316. The wire wrappings are slightly orsufliciently spaced to permit the coating material to slowly ooze ordrip therebetween from the accumulation in the pocket indicated at 316to form the droplets 317. In this instance the discharge or oozing ofthe material from the applicator head is aided by gravity, the dropletsbeing thereupon broken up or developed into finely divided particles bythe electrostatic force developed between the applicator head and thesurface to be coated. Such finely divided particles will there- .upon bedispersed by the electrostatic force over said surface andbe applied tosaid surface. The applicator head can be grounded and the workmaintained at high potential with equally efi'icient results.

By way of example, the arrangement of the overhead applicator of Fig.7is shown diagrammatically in F1g.'9, wherein the source of high voltageindicated at 320 has one terminal grounded at 321 and the other terminalconnected with the applicator head 313 which is thereby maintained athigh potential" relative to the support or electrode, since theelectrostatic force set up therebetween will have the same effect on thedroplets of coating material. Also, it is immaterial as to whether ornot the article to be coated is of conducting or non-conductingmaterial, and such article of non-conducting material is hereinconsidered to be one of the electrodes wherein it is associated with ormasks a grounded support of :conducting material.

The invention claimed is:

1. In apparatus for electrostatically applying liquid coating materialto an article, an atomizing head positioned adjacent the article to becoated, said head comprising a group of elongated members and means forencasing said members and intimately compacting them together, saidmembers projecting for a portion of their length beyond said encasingmeans, means for maintaining between said projecting member portions andthe article an electrostatic field of sufiicient strength both toelectrostatically atomize fine particles from coating material on thesurfaces of said projecting portions and to electrostatically deposit onthe article the particles so atomized, and means for supplying liquidcoating material to said members from their encased ends to the surfacesof said projecting portions at a rate no greater than that at which itis electrostatically atomized.

2. In an apparatus for electrostatically coating an article with aliquid coating material, an elongated, hollow applicator head comprisingsupporting means having thereon a wire wrapping having a series ofspaced turns, portions of which constitute projections and the spacesbetween which constitute restricted orifices through which liquidcoating material can flow to the surfaces of said projections, means forsupplying liquid coating material to the interior of said head, andmeans for creating between said head and an article to be coated anelectrostatic field of sutficient strength both to electrostaticallyatomize finely divided particles from coating material on the surfacesof said projections and to electrostatically deposit upon the articlethe particles so atomized.

3. Apparatus for electrostatically coating an article with a liquidcoating material, comprising a conveyor for moving the article over apredetermined path, a singlefluid atomizing head provided with a liquidsupporting,

flow-guiding surface having a terminus adjacent which liquid coatingmaterial is to be atomized, means for supplying liquid coating materialat a controlled rate to said surface at a point spaced rearwardly fromsaid terminus for flow as an exposed body over the surface to saidterminus for atomization therefrom, and means including a high-voltagesource having its opposite terminals electrically connected to thearticle on the conveyor and the liquid at said terminus for establishingan electrostatic field therebetween capable of atomizing the liquid fromsaid exposed body at said terminus in the form of a spray andelectrostatically depositing the spray on the article while still inliquid st-ate, said head and conveyor being spaced apart by a distancegreat enough to permit the atomized liquid leaving said member to bewidely dispersed. V

4. Apparatus for electrostatically spray-coating an article, comprisingan 'atomizing head, means for feeding liquid coating material to saidhead, means including said feeding means for distributing coatingmaterial to an extended atomizing zone where it is atomized from aplurality of spaced points, said points being sufliciently closetogether to permit the coating material to bridge thespacestherebetween, asupport for supporting an article to be coated inspaced relation to said atomizing zone, and means including ahigh-voltage source for creating over the surface of the article on saidsupport an electrostatic field capable of atomizing the coating materialinto finely divided, electrically charged particles andelectrostatically depositing particles atomized from said atomizing zoneon the article while still in liquid state, said atomizing head andsupport being so relatively disposed as to provide between the articleand the atomizing zone the atomized particles by the electrostaticforces of the References Cited in the file of this patent a spacinggreat enough to permit substantial dispersion of 10 2,685,536

UNITED STATES PATENTS Althouse Sept. 7, 1915 Meston Oct. 26, 1937Formhals Jan. 16, 1940 Gundelfinger Aug. 12, 1941 Starkey et a1 Aug. 3,1954

